The present invention relates to a rigid endoscope and an image transfer optical system for that rigid endoscope.
A viewing optical system for the rigid endoscope generally comprises a relay optical system adapted to transfer images formed through an objective lens to a viewer side wherein an elongate rod lens is used to relay the image odd-numbered times.
A rigid endoscope for the urinary organs of infants and little children has an insert of about φ3 mm. In the industry fields, there is an ultra-fine rigid endoscope having an insert diameter of about φ1 mm to 3 mm that is used for the inside observation or the like of automotive engines.
In order for the fine-diameter rigid endoscope to gain brightness, it is required to implement a lot more relays with an increased NA (numerical aperture).
With a typical prior art endoscope having a lens outer diameter of φ1.1 mm and a total relay length of about 230 mm, nine relays are implemented to achieve NA=0.068.
With such prior arts, however, there are the following problems. As nine relays are implemented with 3 lenses per relay, it requires as many as 27 lenses: this is not preferable for production costs, because of an increased parts count and much time taken for assembling.